Re: [tip:sched/core] sched/numa: Move task_numa_free() to __put_task_struct()

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On Mon, 7 Apr 2014, Mike Galbraith wrote:

On Mon, 2014-04-07 at 10:16 +0200, Peter Zijlstra wrote:
On Mon, Apr 07, 2014 at 09:30:30AM +0200, Mike Galbraith wrote:
-	double_lock(&my_grp->lock, &grp->lock);
+	BUG_ON(irqs_disabled());
+	double_lock_irq(&my_grp->lock, &grp->lock);

So either make this:

	local_irq_disable();
	double_lock();

or


 	for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
 		my_grp->faults[i] -= p->numa_faults_memory[i];
@@ -1692,6 +1693,7 @@ static void task_numa_group(struct task_

 	spin_unlock(&my_grp->lock);
 	spin_unlock(&grp->lock);
+	local_irq_enable();

use:
	spin_unlock()
	spin_unlock_irq()

or so, but this imbalance is making my itch :-)

sched, numa: fix task_numa_free() lockdep splat

Sasha reports that lockdep claims 156654f491dd8d52687a5fbe1637f472a52ce75b made
numa_group.lock interrupt unsafe.  While I don't see how that could be given the
commit in question moved task_numa_free() from one irq enabled region to another,
the below does make both gripes and lockups upon gripe with numa=fake=4 go away.


Hi

I Am hitting this bug quite frequently. I do not see the problem after applying
this patch.

Thanks

Tested-by: Govindarajulu Varadarajan <govindx7c6@xxxxxxxxx>

Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Mike Galbraith <bitbucket@xxxxxxxxx>
---
kernel/sched/fair.c  |   13 +++++++------
kernel/sched/sched.h |    9 +++++++++
2 files changed, 16 insertions(+), 6 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1497,7 +1497,7 @@ static void task_numa_placement(struct t
	/* If the task is part of a group prevent parallel updates to group stats */
	if (p->numa_group) {
		group_lock = &p->numa_group->lock;
-		spin_lock(group_lock);
+		spin_lock_irq(group_lock);
	}

	/* Find the node with the highest number of faults */
@@ -1572,7 +1572,7 @@ static void task_numa_placement(struct t
			}
		}

-		spin_unlock(group_lock);
+		spin_unlock_irq(group_lock);
	}

	/* Preferred node as the node with the most faults */
@@ -1677,7 +1677,8 @@ static void task_numa_group(struct task_
	if (!join)
		return;

-	double_lock(&my_grp->lock, &grp->lock);
+	BUG_ON(irqs_disabled());
+	double_lock_irq(&my_grp->lock, &grp->lock);

	for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
		my_grp->faults[i] -= p->numa_faults_memory[i];
@@ -1691,7 +1692,7 @@ static void task_numa_group(struct task_
	grp->nr_tasks++;

	spin_unlock(&my_grp->lock);
-	spin_unlock(&grp->lock);
+	spin_unlock_irq(&grp->lock);

	rcu_assign_pointer(p->numa_group, grp);

@@ -1710,14 +1711,14 @@ void task_numa_free(struct task_struct *
	void *numa_faults = p->numa_faults_memory;

	if (grp) {
-		spin_lock(&grp->lock);
+		spin_lock_irq(&grp->lock);
		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
			grp->faults[i] -= p->numa_faults_memory[i];
		grp->total_faults -= p->total_numa_faults;

		list_del(&p->numa_entry);
		grp->nr_tasks--;
-		spin_unlock(&grp->lock);
+		spin_unlock_irq(&grp->lock);
		rcu_assign_pointer(p->numa_group, NULL);
		put_numa_group(grp);
	}
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1388,6 +1388,15 @@ static inline void double_lock(spinlock_
	spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
}

+static inline void double_lock_irq(spinlock_t *l1, spinlock_t *l2)
+{
+	if (l1 > l2)
+		swap(l1, l2);
+
+	spin_lock_irq(l1);
+	spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
+}
+
static inline void double_raw_lock(raw_spinlock_t *l1, raw_spinlock_t *l2)
{
	if (l1 > l2)


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